2.1 Geology and Engineering

Question 1

Engineering methodology

Answer 1

Step 1: Problem definition
Step 2: Analysis & Design
Step 3: Construction
Step 4: Operation
Step 5: Decommissioning

Question 2

Overall Goal of Methodology

Answer 2

Site Characterization: provide a model of the sub surface to allow evaluation of designs to meet specific engineering objectives.

Question 3

Essential Geology to consider?

Answer 3

• Stratigraphy
• Sedimentology
• Geo-morphology
• Structure

Question 4

Stratigraphy

Answer 4

• Sequence of Layers
• Order of deposition
• Lateral variation

Question 5

Sedimentology

Answer 5

De-positional processes (wind, water, ice, etc.)

Question 6

Geo-morphology

Answer 6

• Land forms
• De-positional
• Erosional

Question 7

Structure

Answer 7

Deformation after deposition (folding, faulting, jointing)

Question 8

Composition (Mineralogy)

Answer 8

Scientific study of the chemistry, crystal structure, and physical properties of minerals.
Silicate minerals (quartz, feldspars, clays) vs non-silicates (carbonates, oxides, sulphides).

Question 9

Composition (Petrology)

Answer 9

Study of rocks (igneous, metamorphic, and sedimentary) - and the processes that form and transform them

Question 10

Burial History

Answer 10

• Have the particles been reoriented and packed closer together? (compaction increases strength and reduced porosity)
• Have the fluids been expelled? (Consolidation increases strength and reduces porosity)
• Is there any mineral precipitation? (Cementation increases strength and reduces porosity)
• Are the grains joined by cement? (lithification increases strength and reduces porosity)

Question 11

Groundwater (Regional and Local Systems)

Answer 11

Flow occurs on many scales (m to hundreds of km)

Question 12

Groundwater (Aquifers and Aquitards)

Answer 12

• units based on permeability (how easily a fluid can move through the unit), not stratigraphy.

Question 13

Fundamental properties

Answer 13

• Permeability: the ability to transmit fluid through the pore spaces
• Compressibility: the volume change response to load (stress)
• Strength: the ability to carry a load (stress)
• Density: mass/unit volume

Question 14

Structure of the earth: inside out

Answer 14

1. Inner core
2. Core
3. Mantle
4. Crust

Question 15

Inner core

Answer 15

• Mostly solid iron and nickel
• Very high pressures

Question 16

Outer core

Answer 16

• Liquid iron and nickel
• heated by the radioactive decay of U and Th

Question 17

The mantle

Answer 17

• thickest layer
• mostly iron, magnesium, and silicon

Question 18

The crust

Answer 18

• extremely thin, cold and brittle
• composed of siica, aluminum, and oxygen

Question 19

What are minerals?

Answer 19

Naturally occurring in organic crystalline solid that has definite physical and chemical properties.

Question 20

What are rocks?

Answer 20

Naturally formed consolidated material composed of a mixture of minerals.

Question 21

What is the most abundant and important rock forming mineral?

Answer 21

Silicates

Question 22

What minerals are important to engineers because they are strongly resistant to weathering and occur in most soils?

Answer 22

Quartz and feldspars

Question 23

Igneous rocks

Answer 23

Material origin: Crystallized from molten magma
Environment: Underground; and as lava flows
Texture: Mosaic of interlocking crystals
Structure: Massive (structure-less)
strength: Uniform high strength
Major types: Granite, Basalt

Question 24

How to identify whether an igneous rock is intrusive or extrusive?

Answer 24

The rate at which magma cools which is reflected in the rocks texture

Question 25

Intrusive

Answer 25

Form plutons (also called plutonic rock) that cool and solidify underground slowly - large crystals like granite

Question 26

Extrusive

Answer 26

Magma cools rapidly above surface - small crystals like basalt

Question 27

Metamorphic rocks

Answer 27

Origin: Altered by heat/pressure
Environment: Mostly deep inside mountain chains
Texture: Mosaic of interlocking crystals
Structure: Crystal orientation due to pressure
Strength: Variable high; planar weaknesses
Major types: schist, gneiss, slate, marble

Question 28

How to identify metamorphic rocks

Answer 28

Unlike the other two types of rocks, metamorphic rocks start as rocks and then are transformed into different rocks.

Question 29

Sedimentary rocks

Answer 29

Origin: Erosional debris on earth’s surface
Environment: Deposition Basins; mainly sea
texture: mostly granular and cemented
structure: layered, bedded, and bedding planes
strength: variable low; planar weaknesses
Major types; sandstone, limestone, clay

Question 30

Cycle of geology

Answer 30

Processes:
Land - erosion of rock destruction
Marine (ocean, sea) - deposition and forming new sediments
Underground - new rocks created and deformed

Question 31

Relationship between geology and engineering

Answer 31

Geological processes continually modify the earths surface, and add to the complexity of ground conditions. All civil engineering works are carried out on or in ground so its properties and processes are very important to understand.
- Most rocks encountered by engineers are 10 - 500 M years old and they have been displaced and deformed over time.
- Most surface land forms visible today were formed in the last few M years
- This time difference is important because the origin of the rocks at surface may bear NO relationship to the present environment

Question 32

Site investigation

Answer 32

Where most engineers will encounter geology
- Data collection interpretation of ground conditions
- 3D thinking/modeling rendering
- Recognition of hazards/difficult ground conditions
- Understanding how the geology will impact your design (and budget)
- How to manipulate the ground to behave as you need